1. Field of the Invention
The present invention relates to a device, a system and a method for measuring the insulation resistance of an energized electrical apparatus with respect to ground, and therefore also for a diagnosis of insulation loss of such an apparatus.
It is worth noting that, although the present description particularly illustrates the application of the invention to a battery for an electric or hybrid motor by way of example, it will be apparent that the invention is in the same manner applicable to any energized electrical apparatus or system with respect to earth or to a generic reference or safety ground.
The present invention also relates to a self-diagnosis method of the above device.
2. Description of the Related Art
The ever-increasing diffusion in the use of electrochemical batteries with high nominal voltages, for example in electric and hybrid vehicles, results in the possibility of electrical risk associated with the use of such voltages which are potentially dangerous for persons and things. Therefore, the danger associated with the use of electricity, to date considered mainly associated with the use of electricity within working or domestic context, now arises also on electric or hybrid vehicles equipped with storage systems characterized by potentially dangerous electric voltages.
The further diffusion of electrical traction on vehicles, expected in the next few years, associated with the frequent and widespread use thereof for transporting persons and things, could result in the electrical risk and potential danger associated with the use of lithium batteries for traction becoming in the future one of the main causes of risk for the safety of persons using such means of transportation.
Possible drawbacks (such as for example, malfunctioning due to the obsolescence of the components of the electrical apparatus, dielectric breakdown or electric discharges) pose the problem of protection from potentially dangerous events, such as the occurrence of short-circuits or insulation losses, which may cause fires and/or explosions, which may be also particularly serious if they are in the presence of flammable or explosive substances, and such as to even put people's lives in danger.
Among such possible drawbacks, insulation loss of the battery voltage with respect to the earth or to a generic reference or safety ground (such as for example, the chassis of the vehicle) is one of the faults which may occur most frequently.
For example, in the case of a fault due to a cable with a damaged sheath in contact with the vehicle body, a drastic decrease of the insulation resistance is generated between the high-voltage circuit and the vehicle body. Such a decrease in the insulation resistance can be diagnosed by means of an electronic circuit, also of known type, which is capable of detecting the insulation resistance.
Indeed, the use is known in electric and hybrid vehicles equipped with high-voltage systems, of am insulation detection circuit, which is conveniently inserted in the electrical system and is capable of measuring in “run-time” the insulation resistance between the high-voltage circuit and the chassis of the vehicle.
The specific safety and person protection requirements against electrical risks which are applicable to rechargeable energy storage systems on board electric vehicles (both battery-operated electric vehicles and vehicles with “fuel-cells”) and hybrid vehicles are defined in international Standard ISO 6469. Further safety related aspects refer to Standard ISO 26262.
Among the various safety and protection requirements, in ISO 6469, inter alia, the possibility is indicated of using a system for monitoring the insulation resistance by means of an “insulation resistance monitoring system” installed on the vehicle to check the integrity of the high-voltage circuit of the battery by means of a periodic measurement (preferably performed automatically) of the value of the insulation resistance of the battery with respect to earth or to a generic reference or safety ground.
However, the desired functionality of automatically performing the insulation resistance measurement poses the significant technical problem of succeeding in discriminating whether, with respect to an anomalous measurement of the insulation resistance, this is due to a fault of insulation loss of the battery with respect to the ground or to a fault of the insulation resistance measurement circuit itself.
Moreover, the further and even more critical technical problem arises of remediating possible circumstances in which the insulation resistance measurement circuit has failed, or was damaged, or has deteriorated over time, and accordingly is no longer capable of recognizing an insulation loss if this occurs.
With respect to the above, the need is strongly felt for the insulation resistance measurement circuit or system to have effective self-diagnosis functionalities adapted to avoid that a fault in the circuit may compromise the correct detection of the insulation loss.
Additionally, there is an ever-increasing need for accuracy in the measurement of insulation resistance in order to provide accurate information to the battery management system and to render the subsequent safety and protection procedures more timely and effective.
Within the background herein considered, the solutions for the insulation resistance measurement that are currently known and employed do not fully meet the above-illustrated needs and requirements.
Indeed, although the prior art has several solutions for making circuits adapted to measure the insulation resistance of an apparatus with respect to a generic ground or chassis, such known solutions do not resolve, and often do not even consider the issue of the electronic circuit adapted to insulation resistance measurement having a good or increased “diagnosability”. Such an aspect, although underestimated, is very delicate because, as noted above, a breakdown or alteration of the insulation resistance measurement circuit, which in practice is rather frequent, may result in an incorrect detection of fault circumstances that nay be potentially dangerous for the health of people.
In light of the above, the need is strongly felt, mainly within the scope of automobile applications but also within other application scopes (it is easy to understand that similar needs may emerge for energized apparatuses other than a battery and used in other contexts), to provide an electronic measurement device of the insulation resistance that is conveniently designed both to perform the primary task of accurately measuring the value of the insulation resistance and to allow self-diagnosis procedures in order to avoid possible circumstances failed or incorrect detection of insulation loss.